Practically all miniature consumer applications such as hearing aids, mobile phones and similar require microphone assemblies with still larger dynamic range in combination with still smaller size and a low electromagnetic interference (EMI) sensitivity. Smaller size also means a reduced power supply voltage which contradicts the demand for larger dynamic range.
U.S. Pat. No. 6,088,463 describes a silicon-based miniature microphone assembly. It is mentioned, column 3, fines 36-40, that it is possible to produce an embodiment with a diaphragm arranged between two backplates. This may be seen as advantageous in relation to suppress EMI, however, U.S. Pat. No. 6,088,463 does not teach an intention of providing a microphone assembly with a wide dynamic range.
DE 34 13 145 A1 published in 1985, describes an electret condenser microphone assembly suited for replacing a dynamic microphone in a telephone handset. In an embodiment the microphone assembly has a differential electret condenser microphone connected to a differential FET-based preamplifier providing a differential output.
U.S. Pat. No. 6,088,463 is complicated to produce due to the symmetrical diaphragm structure and it does not solve the dynamic range problem. DE 34 13 145 A1 provides a balanced output signal thus providing a high dynamic range. However, the balanced output requires an extra output terminal and thus the solution is unsuitable for miniaturisation in low cost mass production since extra terminals require space and the manufacturing process becomes more complicated and time consuming.
Therefore, it may be seen as an object of the present invention to provide a miniature microphone assembly with an increased dynamic range. The provided microphone assembly should be suitable for low cost production.